Process for obtaining schoenite by direct treatment of kainite containing sodium chloride as an impurity



United States Patent 3,004,826 PROCESS FOR OBTAINING SCHOENITE BY DI-RECT TREATMENT OF KAINITE CONTAINING SODIUM CHLORIDE AS AN IMPURITYGerlando Marullo, Giovanni Perri, Giuseppe Tubiello, and Dante 'Cadorin,all of Milan, Italy, assignors to Montecatini Societa Generale perllndustria Mineraria e Chimica, Milan, Italy No Drawing. Filed July 21,1958, Ser. No. 749,501 Claims priority, application Italy July 22, 19574 Claims. (Cl. 23117) This invention relates 'to a process for obtainingschoenite from crude kainite mineral (KCl.MgSO .3H O) containing sodiumchloride as impurity. It particularly relates to a process comprisingconverting kainite to a mixture of schoenite (K;SO .MgSO .6H O) andsodium chloride, and then separating schoenite from the mixture by meansof a volumetric classification.

.Improved processes for treating kainite mineral have been disclosed inUS. Patents 2,766,884 and 2,766,885 of 1956, to G. Marullo and G. Perri.As indicated by Patent 2,766,884, it is known that kainite can beconverted into schoenite according to the following scheme:

The present invention involves the transformation of the kainiteminerallinto a mixture of schoenite and sodium chloride, followed by avolumetric classification step to separate the schoenite from the NaClcrystals. The transformation reaction of the kainite mineral is carriedout in a saline solution which consists of the mother liquor'obtained bytreating schoenite with water in order to obtain potassium sulfate.

Said mother liquor is obtained in the step of production of potassiumsulfate from schoenite. Schoenite is leached with water at a temperatureof from 48 to 50 G, into a reactor fitted with stirrer.

The ratio of water to schoenite is chosen so as to determine aprecipitate essentially consisting of potassium sulphate; said ratiobeing normally about 0.9.

The separation of potassium sulfate is carried out by means offiltration or centrifugation.

The solution thus obtained is cooled at room temperature (about 20 C.);schoenite precipitates by cooling and it is separated by'filtration orcentrifugation and is successively conveyed to the preparation ofpotassium sulfate.

The mother. liquor obtained .by this last operation is called sulfatemother liquor; itis used for the conversion of kainite into schoenite.

The average composition of such a mother liquor is as follows: I I

The content of chlorine varies from 5 to 7 g./l., while the sodiumcontent is negligible.

The composition of the sulfate mother liquor variesv within narrowlimits because it is obtained from almost pure schoenite with adetermined amountof water at a.

fixed temperature; consequently the variations depend only on theimpurities of schoenite. The K 0 and Mg contents vary at most within +2g./l and -2 g./l. from the above indicated concentrations.

The transformation reaction of kamlte to schoenite 3,004,826 PatentedOct. 17, 1961 ICC Percent Mg 6.6 Cl 28.5 Na 12 K 0 12 the balance tobeing SCH-K 0, with 1.67 parts by volume of sulfate mother liquorcontaining:

G./l. Mg 37.6 K 0 53.7 $0., 207.4

a crystal phase consisting of practically pure schoenite, and a motherliquor, hereafter called intermediate sulfate mother liquor, having thefollowing composition, are obtained:

G./l. Cl Mg 51 K 0 26.25 Na 57 so,

After removing the said practically pure crystal phase (schoenite) bydecantation or filtration, the intermediate sulfate mother liquor isplaced again in the reaction vessel and the remaining kainite mineral isthen added continuously. The total amount of kainite transformable intoschoenite is dependent upon the composition of the final mother liquor,which must achieve an equilibrium with schoenite and NaCl as bottomsubstances (precipitates) About 1 hour after the complete introductionof the mineral, the reaction is complete. This can be determined byanalyzing either the mother liquor or the crystal phase. The finalmother liquors obtained in this second step are discharged.

We made the surprising discovery that in the second step, by carryingout the conversion of kainite into schoenite-i-NaCl under particularworking conditions, schoenite crystals having much greater size than thesodium chloride crystals are obtained. The kainite mineral is addedgradually and the agitation is kept at such limits so as not to cause anexcessive moving.

Upon subjecting the mass of the crystals obtained to a volumetricseparation, the separated portion having higher granulometry consists ofschoenite with low impurities of sodium chloride (from 0.3 to 1% Na),while the very fine portion consists of sodium chloride admixed with allthe slime present in the mineral and with l to 1.5% of K 0.

Thus according to the present invention there is provided an economicalmethod for obtaining schoenite by direct treatment of kainite mineral.The salient feature of the method is as follows. The components of acrystalline mixture of schoenite and sodium chloride, ob-

tained by treating crude kainite with sulfate mother mixture, inaccordance with the present invention there 7 is provided an alternativemethod which permits a better development of schoenite crystals, that isthe formation of larger crystals and in such quantity as to accumulatein them the highest amount of K contained in the crude V kainitemineral.

For this purpose several conversion trials have been carried out in thepresence of substances which could exert influence upon the crystallinegrowth.

It has been found that organic substances such as the primary "aliphaticamines containingo to 15 carbon atoms, and having branched chains,greatly accelerate the formation of large crystals.

7 .After having ascertained such property a complete study'of theseamines has been made, particularly to determine the'lowest' amountneeded in relation to the type ofthe' treated mineral.

Moreover, we made the unexpected discovery that the more or less clayeynature of the mineral does not appreciably modify the activity of saidamines.

As regards the concentration, it has been noticed that it exerts aninfluence alsoasregards the crystalline habitus.

Consequently .the amount. of amine .to' be used depends on the type .ofthe amine, .on the type of crystals to be obtained, further on thepotassium content of the mineral and also on the procedure by which theconversion of 'kainite to schoenite is carried out. i It has been foundthat for akainite mineral containing about 12% K 0, the rest consistingprevalently of sodium chloride, the lowest amount of amine needed inorder to'ob aiii'a remarkable crystalline growth of schoe nitecrystal's'varies "from 200 to 500 g. amine per metric ton ofkainitennneral. i l

'The 'e'fiectof said'annnes has been studied also at temperatur'e'sdieerenrne'm' room temperature and it has been noted that no variationsoccur as regards their activity.

Said amines are used preferably in form of their salts, for example aschlorhydrates or acetates, owing to their more easy dispersion, becausethey are more'soluble than free'amines'. g The'following examplesillustrate the present invention, but are not intended to be limitative.Examples 1, 2 and 3 indicate the results based on tests carried out withthree types of sulfate mother liquors, namely with an intermediatesulfate mother liquor, with a sulfate mother liquor saturated Withsodium chloride, and with a sulfate mother liquor respectively,according to the first embodiment of the invention.

Examples 4a, 5a and 6:: illustrate the alternative method of theinvention, relating to the use of suitable amines for crystallinegrowth. Examples 4b, 5b and 6b correspond to 4a, 5a and 64, but withoutusing amines.

7 EXAMPLE 1 Kainite mineral used:

Granulornetry mm 0.06 K 0 content percent 12 Na 5 content dn 13.5

' Composition of the mother liquor (intermediate mother liquor) used forthe attack:

Product obtained:

Granulometry in mm. Content 5 Class Percent Percent Percent K20 NaEXAMPLE. 2

Kainite mineral employed:

Granulometry mm 0.06 K 0 content percent... 12 N content (l0 Compositionof the mother liquor (intermediate mother liquor) used fortheattack:

G./l. Cl 77 Mg 34.07 80.; 190 K 0 53 Na 50 Product obtained:

Granulometry in mm. Content Glass Percent Percent Percent "EXAMPLE- 3Kainite mineral used:

Granulometry I mm 0.06 K 0 content percent 11 Na. content d0 16.3

Compositon of the mother liquor (sulfate mother liquor) employed .forthe attack:

G./l. K 0 53.7 Mg 37.6 80., 207.4

Product obtained:

Granulometryln I 2 Content Class M Percent Percent Percent Amount of theamine used: 500 g./metric ton crude mineral.

The amide has been employed free, or salified as chlorhydrate oracetate.

Time of reaction: 6 hours.

Composition of the mother liquor (intermediate mother liquor) used:

G./l. C1 140 Mg 51 K 26.25 Na 57 S0 160 (b) Same as Example (a), butwithout using the amine.

Results Trial with amine (4a) Trial without amine (4b) Granulometry oithe product Weight, K10, Na, Weight, K10, Na, Per- Per- Per- Per- Per-Percent cent cent cent cent cent 6 mm.+3 mm- 19. 21. 7 0. 3

11 21. 6 0. 4 25. 4 21. 5 0. 4 12 21. 6 O. 35 13. 0 21. 7 0. 4 2. 7 1S.7 4. 2 7. 8 l9. 4 2. 5 0. 5 3 26 6. 5 16. 5 5. 7 45. 75 1. 3 29. 5 47. 32. 2 28. 3

Similar results have been obtained by using n-octylamine andtrimethyl-pentyl-amine which have been used free or salified withhydrochloric or acetic acid; satisfactory results have been achievedwith n-dodecyl-amine whether free or salified with hydrochloric oracetic acid.

Amount of amine: 400 g. per tone of crude mineral.

Time of reaction: 6 hours.

(b) Same as Example (0), but without using an amine.

Results- 1 Trial with amine (5a) Trial without amine (5b) Granulometry0t the product Weight K10 Na Weight K10 Na Percent Percent PercentPercent Percent Percent EXAMPLE 6 (a) Crude kainite mineral:

Granulometry- Percent 0.l mm 6 (0.1 mm 94 K 0 c n 11.5

Na content 13 Insoluble c ten 1.5

Amine used:

'y-trimethylhexyloxy-n-propylamine CH; CH: CHr-k-CH H-CH:CH7O(CHz)a-NHgTime of reaction: 6 hours.

(b) Same as Example 6(a), but without using an amine.

The process avoids the need for separation of the sodium by flotation inliquids. The separation has been accomplished by ordinary volumetricclassification, such as by standard methods for screening of the solids.

We claim:

1. A process for obtaining schoenite by direct treatment of kainitemineral containing sodium chloride as an impurity, said treatment beingcarried out by means of sulphate mother liquors obtained by treatingschoenite with Water in order to separate potassium sulphate,characterized in that the kainite mineral, ground with a granulometry inthe order of 0.05 to 0.1 mm. is gradually added to said sulfate motherliquors during a time of about 5 hours while stirring moderately so asnot to cause excessive moving, and subsequently still agitating .forabout one hour, thus obtaining a crystal phase consisting of acrystalline mixture of schoenite and sodium chloride, in which thesodium chloride crystals have maintained their original grinding sizewhile the schoenite crystals have a much higher size, in the order of0.1 to 0.75 mm, and further characterized in that the separation ofschoenite from the mixture with sodium chloride is thereafter carriedout by means of a volumetric classification, thus obtaining theschoenite in the portion having higher granulometry.

2. The process of claim 1, the volumetric classification comprising amechanical screening of the schoenite and sodium chloride crystals.

3. A process for obtaining schoenite by direct treatment of kainitemineral containing sodium chloride as impurity, comprising the. steps offorming a sulphate mother-liquor by leaching scho'enite with water inorder 'to separate potassium sulphate, adding a branched primaryaliphatic amine to said liquor, 'commimlting kainite mineral to aparticle size of about 0105 to 0.01 mm., converting the comminutedkainite into a crystalline mixture ofschoenite and sodium chloride bytreatment of said comminuted kaiuite with said sulphate mother liquorconltaining said aliphatic amine to accelerate the crystalline growth ofschoenite, and separating the schoenite crystals from the sodiumchloride crystals by means of volumetric classification.

"ReferencesCitedinthefileofthis patent 1 Q UN TEIi I STATES BATENTS t TI 229,249 7 1O '2,766;885

Cevidalli et al. Sept.1, 1959

1. A PROCESS FOR OBTAINING SCHOENITE BY DIRECT TREATMENT OF KAINITEMINERAL CONTAINING SODIUM CHLORIDE AS AN IMPURITY, SAID TREATMENT BEINGCARRIED OUT BY MEANS OF SULPHATE MOTHER LIQUORS OBTAINED BY TREATINGSCHOENITE WITH WATER IN ORDER TO SEPARATE POTASSIUM SULPHATE,CHARACETERIZED IN THAT THE KAINITE MINERAL, GROUND WITH A GRANULOMETRYIN THE ORDER OF 0.05 TO 0.1 MM. IS GRADUALLY ADDED TO SAID SULFATEMOTHER LIQUORS DURING A TIME OF ABOUT 5 HOURS WHILE STIRRING MODERATELYSO AS NOT TO CAUSE EXCESSIVE MOVING, AND SUBSEQUENTLY STILL AGITATINGFOR ABOUT ONE HOUR, THUS OBTAINING A CRYSTAL PHASE CONSISTING OF ACRYSTALLINE MIXTURE OF SCHOENITE AND SODIUM CHLORIDE, IN WHICH THESODIUM CHLORIDE CRYSTALS HAVE MAINTAINED THEIR ORIGINAL GRINDING SIZEWHILE THE SCHOENITE CRYSTALS HAVE A MUCH HIGHER SIZE, IN THE ORDER OF0.1 TO 0.75 MM., AND FURTHER CHARACTERIZED IN THAT THE SEPARATION OFSCHOENITE FROM THE MIXTURE WITH SODIUM CHLORIDE IS THEREAFTER CARRIEDOUT BY MEANS OF A VOLUMETRIC CLASSIFICATION, THUS OBTAINING THESCHOENITE IN THE PORTION HAVING HIGHER GRANULOMETRY.